During transfer of liquid or gas from a subsea pipeline or other installation at great ocean depths to a floating structure by riser devices, high loads must be endured thereby due to currents, waves, or motions of the structure. Furthermore, rather strong internal wear caused by the flowing fluids, as well as external corrosion, will tend to shorten the useful lives of the riser devices.
In Norwegian Pat. No. 136 243 an articulated riser device is suggested which comprises fluid conducting lines which are rigidly connected to a part which is connected to similar parts by means of universal joints. Such a riser device is not a very stable structure and will experience relatively large horizontal and vertical motions due to comparably small forces, and the device will thus be subjected to oscillations which entail danger for subsequent fatigue and failure of the parts of the structure.
Internal wear from the conveyed fluid and external corrosion have lately turned out to be more extensive than previously assumed, and maintenance requirements are therefore constantly being made more stringent. Thus, the previously known riser devices will have to be replaced relatively often. This entails considerable expenditures, while time consuming replacement work leads to large production losses.
The object of the present invention is to provide a riser device of the type mentioned by way of introduction, which device eliminates, or to a large extend reduces the noted drawbacks and deficiencies. A detailed understanding of the invention will be obtained by reference to the following discussing taken in conjunction with the accompanying drawings.